1. Field of the Invention
The present invention relates to a communications system that utilizes networks and operates based on Internet Protocol. Further, the present invention relates to a method of controlling the communications system, and to a computer program used for managing the communications system.
2. Description of the Related Art
Networks based on Internet Protocol (‘IP’) have been used for a data communications system involving clients and servers connected to each other. Through the networks, each client can obtain various kinds of information. For instance, the client can view home pages and send or receive messages by E-mail. Upon receiving a request from the client, the server automatically sends back desired information to the client.
In the communications system, data congestion may occur when many clients try to access one particular server simultaneously. If such access concentration occurs, the supply of information to the client from the server may delay, and the quality of service by the server will deteriorate. What is worse, the amount of data to be process can be beyond the server's capacity, thereby breaking down the whole system.
Once the system stops functioning properly, the clients, who have no effective countermeasures against it, cannot help waiting for the system to return to the normal state. On the side of the server, to restore the system, the requests supplied from the clients may partially or entirely discarded, so that the amount of the work to be done is reduced below the server's capacity. Apparently, such destruction of the clients' data is not preferable.
One way to overcoming the data congestion or access concentration is to increase the data transfer rate on the networks, or to improve the data-processing capacity of the server However, the improvement of the data transfer rate or server's capacity is not a feasible option since it will lead to an increase in facility costs and therefore are not feasible options.
JP-A-10(1998)-200581 discloses a technique of avoiding IP packet congestion. Specifically, according to this conventional technique, a plurality of routers disposed between different networks are adjusted so that their data-receiving rate is reduced. This makes the data transfer scarcer, and therefore contributes to the prevention of IP packet congestion.
The above conventional technique, however, cannot prevent access concentration on a router or server. What is worse, once the access concentration occurs at a particular router for example, the network apparatuses adjacent (in a network-topological sense) to the router will be affected by the access concentration. For instance, the data-processing speed of the adjacent network apparatus can become unacceptably slower.